Differentiated cardiomyocytes do not divide and therefor, do not regenerate functional muscle after injury, It is therefor important to identify cell populations with the potential to differentiate into cardiomyocytes and thus repair damaged heart muscle. A promising source of potential replacement cardiomyocytes is a stem cell population known as SP (or side population). SP cells are FACS purified based on high efflux of the dye Hoechst 33342. These cells have been isolated from the bone marrow, umbilical cord blood, and skeletal muscle of various animal sources and can contribute to both muscle and hematopoietic lineages in mice hosts. The full potential of SF cells to differentiate is largely untested. It is unclear whether the tissue source pre-disposes them to particular differentiation programs. Similarly, it is unclear what effect local environmental cues have on their differentiation. I will carry out a series of experiments, grafting SP cells from quail donors to different locations in young chick hosts. This will reveal if SP cells can develop into a broad range of cell types when exposed to different sets of developmental signals. This will also tell us if SF cells can differentiate into functional cardiomyocytes upon exposure to the correct environmental cues.